1. Field of the Invention
The present invention relates to an electronic endoscope apparatus to be inserted into a subject for inspection to enable its inside to be observed.
2. Related Art And Prior Art Statement
Endoscopes have been widely used, each of which comprises an elongated insertion portion to be inserted into the coelom to observe the internal organ in the coelom, and which uses a curing tool inserted into a channel for the curing tool to perform a variety of treatments, if necessary.
Also industrial endoscopes have been widely used for the purpose of observing and inspecting internal flaws or corrosion occurring in boilers, gas turbine engines, pipes in chemical plants and the bodies of automobiles.
Further, a variety of electronic endoscopes have been used each of which has an image pickup means comprising a solid-state image sensing device, such as a charge-coupled-device (CCD).
FIG. 1 illustrates an example of the structure of an electronic endoscope apparatus which uses an electronic endoscope 81. The electronic endoscope 81 has an elongated and, for example, flexible insertion portion 82. Further, a control portion 83 having a large diameter is connected to the trailing end of the insertion portion 82. A flexible cable 84 is extended sidewards from the trailing end of the control portion 83, the cable 84 having a connector 85 in the leading portion thereof. The electronic endoscope 81 is connected to a video processor 86 via the connector 85, the video processor 86 including a light source device serving as an irradiation-light generating means and a signal processing circuit. Further, a monitor 87 is connected to the video processor 86.
The insertion portion 82 has, in the leading portion thereof, a hard leading portion 89 and a warp-enabled portion 90 which can be warped and which is disposed sequentially, the warp-enabled portion 90 being disposed adjacently to the trailing portion of the leading portion 89. Further, the endoscope 81 has an arrangement that a warp-control-portion knob 91 disposed in the control portion 83 can be rotated so that the warp-enabled portion 90 is warped horizontally or vertically. The control portion 83 has an insertion port 92 communicated with a channel (omitted from illustration) for a curing tool disposed in the insertion portion 82.
As shown in FIG. 2, a light guide 94 for transmitting irradiation light is arranged to penetrate the insertion portion 82 of the electronic endoscope 81. The leading surface of the light guide 94 is disposed in a leading portion 89 of the insertion portion 82 so that irradiation light can be emitted from the leading portion 89. The light-incidental end of the light guide 94 is passed through the universal cord 84 and connected to the connector 85. The leading portion 89 has an objective lens system 95 fastened thereto. A solid-state image sensing device 96, such as CCD, is disposed at a position at which an image is formed by the objective lens system 95. The solid-state image sensing device 96 has sensitivity in a wide range from the ultraviolet region to the infrared region including a visible region. Signal lines 71 and 72 are connected to the solid-state image sensing device 96, the signal lines 71 and 72 being passed through the insertion portion 82 and the universal cord 84 as to be connected to the connector 85.
On the other hand, a lamp 73 serving as an irradiation light source for emitting light in a wide band zone from ultraviolet rays to infrared rays is disposed in the video processor 86. The lamp 73 may be an ordinary xenon lamp, a strobe lamp or a halogen lamp. The xenon lamp, the strobe lamp and the halogen lamp are able to emit ultraviolet rays and infrared rays by a large quantity as well as visible rays. The lamp 73 is supplied with electric power from a light source portion 77. Light emitted from the lamp 73 is made incident upon the light-incidental end of the light guide 94 and guided to the leading portion 89 via the light guide 94. As a result, light is emitted from the leading portion 89 so that the portion to be observed is irradiated with light.
Irradiation light is then returned by the portion to be observed, and it is imaged on the solid-state image sensing device 96 by the objective lens system 95 so that returned light is photoelectrically converted. The solid-state image sensing device 96 is, via the signal line 71, applied with drive pulses from a driver circuit 70 disposed in the video processor 86. A video signal is read from the solid-state image sensing device 96 in response to the drive pulse to transfer the video signal.
The video signal read from the solid-state image sensing device 96 is, via the signal line 72, supplied to a pre-amplifier 74 disposed in the video processor 86 or in the electronic endoscope 81. The video signal amplified by the pre-amplifier 74 is supplied to a processing circuit 75 to be subjected to signal processes, such as a .gamma.-correction process and a white balance process. As a result, the video signal is transmitted as R, G and B signals and as well as supplied to an encoder 76. The encoder 76 subjects the R, G and B signals to conversion processes to transmit an NTSC composite signal.
The white balance operation is so controlled that, if a white subject is imaged for example, the values of the transmitted R, G and B signals are the same.
The R, G and B signals or the NTSC composite signal is supplied to a color monitor 87 so that the observed portion is color-displayed by the color monitor 87.
It can be considered that the foregoing conventional example encounters the following problems in a case where the type of the light source serving as information about the irradiation light generating means, for example, the type of the lamp, is changed. The lamp for the endoscope is typified by the foregoing xenon lamp and the halogen lamp. The xenon (Xe) lamp and the halogen lamp have different radiation energy distributions and also exhibits a difference in the color temperature of about 2000K. If the color temperature is considerably different by the foregoing degree, the white balance adjustment performed to adjust the color reproduction is insufficient to realize satisfactory reproductions of the other colors. In general, the xenon lamp is used as a usual lamp and the halogen lamp is used as an emergency lamp.
What is worse, a signal processing method must be varied between different irradiation (imaging) methods, which are the types of the light sources serving as information about the irradiation-light generating means, for example, between a plane sequential method and a single-plate color method (hereinafter sometimes expressed as a "simultaneous method"). The conventional structure cannot cope with the foregoing problem.
Since medical endoscopes among the endoscopes for use in a variety of fields are so used that the inner wall of the body is the subject of imaging, the reproduced color has a feature that red shades are made relatively thick. Therefore, if the distance from the leading portion of the endoscope to the subject is elongated, a major portion of irradiation light emitted from the light guide is applied to the subject after light has been reflected by the inner wall. Hence, red shades are intensified excessively in the colors of the imaged subject. That is, the image is affected by so-called secondary reflected light.
Some light source devices have a light-quantity adjustment means, such as a diaphragm, for the purpose of obtaining a proper light quantity. The position of the diaphragm, which is the operational state of the light source, or a deflection between the diaphragm and the optical axis sometimes varies the color of irradiation light emitted from the lamp. Therefore, there arises a problem in that the diaphragm is changed due to the brightness of the subject and the change in the brightness changes the overall color even if the white balance adjustment is performed.
An electronic endoscope adapted to the plane sequential method has an arrangement that a color-decomposing rotative filter is disposed in the light source. If the color-decomposing rotative filter has been changed, the color reproducibility of the obtained image depends upon scatter of the spectrum characteristics of the filter. The conventional apparatus has an arrangement that the scatter of the color-decomposing filter is adjusted by only the white balance adjustment. Therefore, the colors, which are critical for making a diagnosis with the endoscope, have not been collected satisfactorily.
There has been a light source device of a type having three types of irradiation modes, that is, a plane sequential method/a single-plate color method/an optical-type-endoscope so that the mode is changed over in accordance with the type of the endoscope and that of the processor that are combined at the time of using. In the case where a processor adaptable to both plane sequential method and the simultaneously method is combined with a light source device at the time of use, a system is desired that is able to efficiently and correctly set each device and exhibits excellent operational facility.
In an electronic endoscope apparatus capable of processing image signals respectively obtained by the plane sequential method and the simultaneous method, the signals respectively obtained by the two methods have different forms. Therefore, the signal process, for example, a white balance processing operation and the like must be changed to be adaptable to the foregoing methods.
Further, the wave detection method for generating a signal for controlling the gain must be changed in an AGC (Automatic Gain Control) provided for the processor portion to be adaptable to the different modes, that is, the plane sequential mode and the simultaneous mode, which is one of the operational states of the light source.
In the conventional electronic endoscope apparatus, drive of the CCD thereof cannot be changed to be adaptable to a state whether the light source is the light source for the plane sequential irradiation light or the light source for the white light irradiation. Therefore, the resolution has deteriorated or the dynamic range has fallen undesirably.
A light source device solely adaptable to the plane sequential method encounters an undesirable color mixture if the rotational speed of a rotative filter for separating irradiation light into a plurality of different wavelength regions is changed. If the numerical aperture of an optical filter disposed in the rotative filter is changed, light is undesirably introduced and a flicker and/or a color mixture takes place. If the sequential order or the configuration of colors of the optical filter is changed, an undesirable color mixture takes place. Each of the foregoing facts is one of the operational states of the light source.
Some of the electronic endoscope apparatuses use special light, such as infrared rays, for the purpose of observing, for example, blood flows as well as performing the imaging operation using plane sequential irradiation light and white irradiation light.
In the case where the special-light observation is performed, the white balance realized in a usual observation operation has been insufficient to always obtain color tone that is suitable for the observation.
If the xenon lamp, which is the usual lamp of the light source device, is burned out and, accordingly, changing over to the halogen lamp serving as the emergency lamp is performed, the signal processing operation of the processor has not been changed. Therefore, if changing over to the emergency lamp is performed during an inspection, color is rapidly changed. Therefore, the observation rapidly becomes difficult to be performed, causing a problem to rise at the time of performing the inspection.
The lamp serving as the emergency lamp emits light by a quantity smaller than that emitted by the diagnosis irradiation xenon lamp. Therefore, there arises a problem in that the observed image is darkened when the emergency lamp is used.
Further, setting, in which the white balance arranged with the xenon lamp is as it is used, has been employed at the time of performing the process although the lamp, which is being lit, is the halogen lamp. Therefore, the obtained image is excessively reddened.
Since a precise inspection cannot be performed under the emergency lamp as described above, only removal of the endoscope has been performed usually in order to secure safety of a patient.
In order to obtain a further excellent image, a countermeasure must be taken against the reduction in the light quantity of the lamp due to an aged deterioration as well as that against the life and a failure of the lamp. For example, the light quantity of a xenon lamp for use in the light source device is in inverse proportion to the time in which the xenon lamp is lit. Therefore, the light quantity of the light source becomes changed by a quantity of two times or more before and after the lamp is changed.
Hitherto, the automatic light regulation loop characteristics of irradiation light has been set while making a lamp which has been lit for tens of hours to be a standard. Therefore, the light regulation loop gain is undesirably set to a low level due to lack of the light quantity immediately before a new lamp is installed. As a result, the response is delayed excessively. On the other hand, the light regulation loop gain is raised excessively due to an excessively large light quantity immediately after the change of the lamp. Therefore, tendency of hunting rises.
When the light regulation operation is performed, the relationship between the diaphragm blade and the optical path, that is, the degree of the diaphragm (the position of the diaphragm) sometimes changes the color of irradiation light. Therefore, there arises a problem that the color tone is changed.
What is worse, the relationship between the reduction in the light quantity of the lamp and the AGC (Automatic Gain Control) of the processor raises the following problem.
The processor of an electronic endoscope apparatus usually performs the AGC in order to maintain a signal obtained by performing imaging with a CCD at a predetermined level. However, if the AGC is performed in a case where the light quantity of the lamp has been reduced, noise becomes conspicuous. In particular, the abnormality of the color tone becomes conspicuous when the usual lamp has been changed over to the emergency lamp.
As for the operation of the AGC, another problem arises due to the relationship between it and the diaphragm serving as a light quantity adjustment means for the light source.
There has been available an apparatus for displaying the image of an endoscope of a type which simultaneously displays a parent image plane and a child image plane. The foregoing apparatus usually displays a kinetic image by only the parent image plane thereof. However, it is convenient for an observer to also display the kinetic image in a case where a still image is displayed. Accordingly, an apparatus has been suggested which displays a kinetic image on either image plane thereof and which displays a still image on the residual image plane.
In the foregoing apparatus, when freezing is performed in a CCD shutter mode, the iris (the blade) of the diaphragm provided for the light source device is operated in order to give the CCD a proper exposure light quantity. As a result, the diaphragm is opened. However, if proper brightness cannot be obtained due to a too long observation distance, flash irradiation has been performed at the time of freezing. When, for example, the child image plane is displaying a kinetic image at this time, the AGC reacts with the flash irradiation. Therefore, an unsightly image such as hunting is displayed.
Although the AGC acts to maintain the signal level at a predetermined level in response to light reflected by a subject, it encounters the foregoing problems depending upon the state of the diaphragm and/or that of the irradiation light source. The conventional structure has no means adaptable to each of the states of the light source device and a plurality of irradiation modes.
What is worse, the conventional electronic endoscope apparatus cannot properly control the light quantity if a light source having no light quantity adjustment means is connected in place of a light source having a function capable of automatically regulating light. In this case, a normal image cannot be obtained.
In addition, the conventional endoscope apparatus encounters a fact that its diaphragm is opened in a case where trans-illumination takes place in the light source. As a result, the light quantity cannot be controlled and the brightness of the image is undesirably saturated.
As described above, if a variety of countermeasures are not taken to be adaptable to information about the irradiation light generating means such as the type, the operational state or the function of the light source, problems of deterioration in the image quality and efficiency and the like arise.